Use opt in package repo mirror in gate
Use opt in package repo mirror in gate

OpenStack CI would prefer to not have the ceph repo package mirror
enabled by default for all jobs. Instead the mirror config will be
provided in a directory that apt won't read and can by copied/linked
into the dir that apt will read.

This gives testing greater flexibility and prevents growing dependencies
on non standard repos in jobs that don't intend on growing those
dependencies.

Change-Id: Icd87013fa74601268c19a8b79abf6b7baeaca9db
Depends-On: I410f45064080e1bb93684899028e9af34bd555a1

openstack/devstack-plugin-ceph,ajarr/devstack-plugin-ceph